The invention relates to an X-ray diagnostic installation for X-ray tomographic images, comprising at least one X-ray source for generating an X-ray beam, comprising a control generator for effecting movement of the X-ray beam for the purpose of irradiating the patient from various directions, comprising a patient support, comprising an X-ray image intensifier which is surrounded by deflection coils which are connected wih a deflection device (connected to the control generator) for effecting the synchronous movement of the electron image in the X-ray image intensifier, and comprising a television chain coupled to the output of the X-ray intensifier. With this X-ray diagnostic installation one obtains X-ray tomographic images of body layers extending in a longitudinal direction of the patient.
In the German OS No. 27 12 320 (U.S. Pat. No. 4,149,082 issued Apr. 10, 1979) such an X-ray diagnostic installation is described in which, by means of a synchronous movement of the X-radiation and of the image field of the X-ray image intensifier, a body layer can be sharply imaged whereas all other body parts not lying in this layer are suppressed through lack of sharp definition. The desired layer can be selected through the alteration of the deflection of the electron image in the X-ray image intensifier. Two coil pairs, arranged about the X-ray image intensifier, generate a magnetic field which effects the deflection of the electron image of the X-ray image intensifier.
The two coil pairs are arranged about the X-ray image intensifier; the coils are energized corresponding to the range of deflection of the electron image in the X-ray image intensifier; the level of energization of the coils is dependent upon the required maximum layer height (or level); and the coils must, under certain circumstances, be subjected to high currents so that distortions of the magnetic field may occur which impair the resolution of the tomographic image. These distortions restrict the possible layer height range. In addition, high demands are here made of the X-ray image intensifier. Even small differential distortions which, in particular, occur in the direction of the border of the X-ray image intensifier, restrict the usable range of the input image of the X-ray image intensifier, as a consequence of which the maximally possible layer height is further reduced. Furthermore, during the utilization of, for example, rectangular waveform currents for the deflection coils, comet tail-shaped image distortions occur which likewise impair the resolution of the X-ray tomographic image.